Magnetron tube



Nov. 29, 1960 J GROHE MAGNETRON TUBE Filed Aug. 21, 1959 INVENTOR.

EDWARD J GROHE a fizw A TTORNE Y 2,962,618 MAGNETRON TUBE Edward J. Grohe, Bound Brook, N.J., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan 'Filed Aug. 21, 1959, Ser. No. 835,207 11 Claims. (or. 313-157 This invention relates to magnetron-type electron discharge tubes and to improvements in the construction of such tubes, and particularly to means for producing the desired magnetic field therein.

One form of magnetron tube, to which the principles of the invention apply, includes an electrode assembly which comprises an elongated central cathode and a plurality of groups of elongated electrodes surrounding the cathode and secured together at their opposite ends by means of insulating end disks or plates. All of the electrodes are substantially parallel to each other. A cylindrical magnet surrounds the electrode assembly and provides a magnetic field oriented longitudinally in the tube. In operation of this type, a beam of current flows from the central cathode to one of the groups of electrodes at a time, and this beam may be switched from one group of electrodes to the next. It has been found that some of the electrons in the beam from the cathode tend to flow toward the ends of the electrode assembly where they strike the insulating end disks which support the electrodes. This electron bombardment of the insulating disks causes them to become electrically charged, with the result that the electric field in the tube becomes distorted and electron flow is adversely affected.

The objects of the present invention are concerned with an improved construction for a magnetron tube in which electron flow is controlled and spurious effects on the magnetic and electric fields in the tube are minimized and tube operation is improved,

In brief, a magnetron-type electron tube embodying the invention comprises, in a suitable envelope, an electrode assembly including a central longitudinally elongated cathode electrode surrounded by groups of longitudinally elongated electrodes which are adapted to form and receive an electron beam from the cathode. The various electrodes are secured together parallel to each other by means of insulating end disks secured to the opposite ends of the electrodes. A cylindrical permanent magnet surrounds the tube envelope and the electrodes contained therein, and the axis of the magnet is coaxial with the longitudinal axis of the envelope and the electrode assembly. The magnet provides a longitudinal magnetic field in the envelope which combines with the electric field therein to control the fiow of electrons from the cathode to the groups of electrodes.

According to the invention, means are provided associated with the electrode assembly, to control the flow of electrons so that they strike the electrodes substantially at their centers and are substantially prevented from fanning out and striking the insulating end plates of the electrode assembly. Thus, the end plates do not become electrically charged and they do not adversely affect electron flow.

The desired result is achieved, according to the invenion, by providing within the envelope pieces of material which affect the magnetic field provided by the permanent magnet and which are properly positioned to provide the desired configuration for this magnetic field. The prenite States Patent F 2,962,618 cfi Patented v, 2s, 1.960

ferred material has high magnetic permeability but is not permanently magnetized. According to one arrangement, the pieces of material are secured to the outer surfaces of the target electrodes. In order to provide the desired magnetic field configuration toprevent an electron beam from fanning out as described above, the tabs of mag- 'letically permeable material are aligned on a common circumference so that, in eifect, they form a broken ring surrounding approximately the center of the electrode assembly.

The invention is described in greater detail by reference to the drawing wherein:

Fig. 1 is a perspective view of a magnetron beam switching tube embodying the invention; and

Fig. 2 is an elevational view of a portion of the tube of Fig. 1 showing the orientation of some of the magnetic flux lines as they appear both with and without the invention.

The principles of the invention are applicable to magnetron tubes and, particularly, to a magnetron beam switching. tube, Type 6700. This type of tube is shown in Fig. 1 as tube 10 and includes, briefly, an envelope 12 which contains an electrode assembly 13 including a central longitudinally elongated cathode 14 and ten groups of electrodes spaced radially equidistantly from the cathod'e and surrounding the cathode and parallel to each other and to the cathode. Each group of electrodes includes a generally U-shaped elongated spade electrode 16 and a generally L-shaped target electrode: 13 positioned so that each target occupies the space between adjacent spade electrodes. The targets have outer surfaces 19. Each spade electrode serves to form and hold an electron beamon its associated target electrode. A generally rodlike switching electrode 20 is also included in each group of electrodes and is positioned between one edge of each target electrode and the adjacent spade electrode. The switching electrodes are known as switching grids. The electrodes of the assembly 13 are secured together by meaiis of top and bottom insulating end disks 22. and 24, respectively, of mica or the like, which are accessible to electrons flowing from the cathode to the other electrodes.

An open-ended cylindrical permanent magnet 26 is provided surrounding the tube envelope and coaxial therewith. The magnet is secured to the tube envelope in any suitable-manner, for example, by means of a layer 28 of a suitableplastic material. The magnet providesan axial magnetic field which is utilized in conjunction with electricfields within the tube to form and switch an electron beam from thecathode to each of the groups of electrodes. The direction in which the beam switches, that is clockwise or counter-clockwise, is always the same and is determined by the orientation of the electric and magnetic fields.

Briefly, in operation of the tube It), electrons emitted by the cathode are retained at the cathode if each of the spades, targets and switching grids carries its normal operating electrical potential. When a spade or switching grid experiences a suitable lowering of its potential, an electron beam is formed and directed to the corresponding target electrode. Ordinarily, with a cylindrical magnet, the electrons in the beam tend to flow out toward the ends of the electrode assembly 13 and, addition, some electrons strike the top and bottom mica disks 22 and 24. Such electron bombardment of the mica disks would ordinarily cause the disks to become electrically charged and then adversely affect electron flow in the tube.

According to the invention, the configuration of the longitudinal magnetic field provided by the magnet 26 is modified to provide the proper configuration to achieve the desired electron flow. The desired. magnetic field configuration is achieved by means of tabs 3t) of conductive material properly positioned within the tube envelope 12. The tabs are preferably of a material which has high magnetic permeability but cannot be permanently magnetized during tube operation. One such material is soft iron.

For support within the tube envelope 12, the tabs 30 are welded or otherwise secured to the outer surfaces 19 of the target electrodes 18. The target electrodes are selected for supporting the tabs because they are the most accessible electrodes of the electrode assembly 13. The tabs 30 might also be secured to the spade electrodes, or elsewhere, if convenient. In order to maintain electron flow at about the center of the electrode assembly, the tabs are secured to approximately the center portions of the targets and they are substantially aligned on a common circumference. In addition, the tabs are preferably as wide as the target surface to which they are secured and they are approximately one-third as long as the targets.

This orientation of the tabs 30 causes the flux lines, which would ordinarily be substantially straight lines as shown by the dotted lines 32, to bend as shown by the solid lines 34. Of course, if other magnetic field configurations are desired, the tabs 30 may be arranged differently than in the manner described above.

What is claimed is:

1. A magnetron tube including an envelope, an electrode assembly in said envelope, said electrode assembly having a longitudinal orientation in said envelope, magnet means providing a longitudinal magnetic field in said envelope, and magnetic means provided in said envelope for modifying the magnetic field produced by said magnet means, said magnetic means comprising separate pieces of magnetic material secured to individual electrodes of said electrode assembly.

2. A magnetron tube including an envelope, an electrode assembly in said envelope, said electrode assembly having a longitudinal orientation in said envelope, magnet means providing a longitudinal magnetic field in said envelope, and magnetic means provided in said envelope for modifying the magnetic field produced by said magnet means, said magnet means comprising separate pieces of magnetic material secured to individual electrodes of said electrode assembly and oriented properly to modify the configuration of said longitudinal magnetic field so that electrons are retained substantially at the center of said electrode assembly.

3. A magnetron tube including an envelope, an electrode assembly in said envelope, said electrode assembly having a longitudinal orientation in said envelope, magnet means providing a longitudinal magnetic field in said envelope, and magnetic means provided in said envelope for modifying the magnetic field produced by said magnet means, said magnetic means comprising separate pieces of magnetic material secured to individual electrodes of 4 said electrode assembly and oriented on a common circumference surrounding said electrode assembly in the vicinity of the center thereof.

4. A magnetron beam switching tube including an envelope containing an electrode assembly comprising a cathode and a plurality of groups of electrodes; each group of electrodes including a target electrode which receives an electron beam and produces an output signal therefrom, a spade electrode which holds an electron beam on its associated target electrode, and a switching electrode which serves to switch an electron beam from one group of electrodes to the next; said electrode assembly having a longitudinal orientation in said envelope, magnet means providing a longitudinal magnetic field in said envelope, and magnetic means provided in said envelope for modifying the magnetic field produced by said magnet means.

5. The tube defined in claim 4 wherein said magnetic means comprises separate pieces of magnetic material.

6. The tube defined in claim 4 wherein said magnetic means comprises separate pieces of magnetic material of high magnetic permeability and not permanently magnetized.

7. The tube defined in claim 4 wherein said magnetic means comprises separate pieces of magnetic material secured to individual electrodes of said electrode assembly.

8. The tube defined in claim 4 wherein said magnetic means comprises separate pieces of magnetic material secured to individual electrodes of said electrode assembly and oriented properly to modify the configuration of said longitudinal magnetic field so that electrons are retained substantially at the center of said electrode assembly.

9. The tube defined in claim 4 wherein said magnetic means comprises separate pieces of magnetic material secured to individual electrodes of said electrode assembly and oriented on a common circumference surrounding said electrode assembly in the vicinity of the center thereof.

10. The tube defined in claim 4 wherein said magnetic means comprises separate pieces of magnetic material secured to each target electrode.

11. The tube defined in claim 4 wherein each target electrode is the outermost electrode of each group of electrodes and each target has an outer surface facing said envelope and a separate piece of magnetic material secured to the outer surface of each target at about the center of the target.

References Cited in the file of this patent UNITED STATES PATENTS Espe Mar. 18, 1941 2,609,522 Hull Sept. 2, 1952 2,721,955 Sin-Pih Fan Oct. 25, 1955 

